Add RelWithDebInfo target.

[shane-lawrence]

Signed-off-by: Shane Lawrence [email protected]

What type of PR is this?
/kind feature

Any specific area of the project related to this PR?
/area build

What this PR does / why we need it:
Debug binaries can behave differently from release binaries, which can make it hard to reproduce Release bugs in a Debug environment for certain edge cases. However, the release target doesn't produce debug symbols so it is difficult to trace certain kinds of bugs.

This PR adds the cmake-standard RelWithDebInfo target so we can create a binary that behaves exactly the same as the release target but has debug symbols available in a separate file.

Which issue(s) this PR fixes:
Fixes #2268.

Special notes for your reviewer:
This PR requires additional testing to ensure that the binary really is the same as the release binary. This first attempt might also need additional changes to conform to the existing style and good coding practices for this project.

Does this PR introduce a user-facing change?:
NO

NONE

[poiana]

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This pull-request has been approved by: shane-lawrence
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[shane-lawrence]

I've only tried to remove debug symbols from the original binary, but I'm seeing a substantial change in file size compared to the release binary. Building with bundled deps and no specified CMAKE_BUILD_TYPE (defaults to Release), I get a userspace/falco/falco binary that's 398MB. Building with CMAKE_BUILD_TYPE=RelWithDebInfo, I get a userspace/falco/falco.debug file that's 222MB and a userspace/falco/falco binary that's 90% smaller at only 26MB. The binary seems to work the same though.